Electrode support structure utilizing a corregated metal ribbon for accomodating thermal expansion

ABSTRACT

A corrugated metal ribbon is attached between the outer circumference of a planar grid or cathode electrode and the interior opening of a contact member, the corrugated member accommodating thermal expansion differentials without distortion of the electrodes or contact members so that the electrodes that can be mounted and maintained in precise spaced relationship.

United States Patent James E. Beggs Schenectady, N.Y. [21] AppLNo.810,951

[72] Inventor 8 800 X X 8 9 33 2 133 3 ll. 3 l .1. 3

3/1958 Cut1er...........

2,832,911 4/1958 VanVe1zer....

3,158,122 11/1964 DeGive......... 3,334,263

[22] Filed Mar. 27, 1969 [45] Patented Feb. 16, 1971 [73] AssigneeGeneral Electric Company 8/1967 Beggs.......................:::. PrimaryExaminerRoy Lake Assis!an! Examiner-E. R. LaRoche n, Julius .1 n, FrankL. Neuhauser and Awe mmw

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ABSTRACT: A corrugated metal ribbon is attached between cc of a planargrid or cathode electrode g of a contact member, the corrugated ingthermal expansion differentials 14 Claims, 2 Drawing Figs.

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ELECTRODE SUPPORT STRUCTURE UTILIZING A COR- REGATED METAL RIBBON FORACCOMMODATING THERMAL EXPANSION ELECTRODE SUPPORT STRUCTURE Thisinvention relates to high frequency electron discharge devices and, inparticular, to a support for the electrode of such a device so that theycan be operated over a broad power and temperature range withoutdisturbing the precise spacing between the electrodes.

In my U.S. Pat. No. 2,680,824, assigned to the assignee of the presentinvention, a type of electron discharge device having planar electrodesis described and claimed, which device may be miniaturized in structureand provided with externally accessible ringlike terminals. Theseminiaturized discharge devices are useful at high frequencies becausetheir electrodes are small in cross section and relatively closelyspaced, thereby reducing interelectrode capacitance and electron transittime between electrodes. While this construction per- -mits operation athigh frequencies, there is always the desire to obtain even greaterpower output at such high frequencies. To accomplish such an objectiverequires operating at still greater current densities at which the finewires of the grid electrodes tend to distort because of the inability toadequately cool the grid. Consequently, it is desirable to obtain astruc ture inwhich heat is rapidly removed from the grid electrode toprevent such distortion and yet to provide a structure which allowsaccurate spacing of the grid electrode with respect to the cathode andwhich is not distorted when operating at high temperatures.

Another practice in building planar-type electron discharge devices isto mount the cathode on a cylinder of thin metal. When such a cathode isheated, the cylinder elongates and moves the cathode surface closer tothe grid surface. To obtain high performance from such a device, it isnecessary to operate with the cathode in close proximity to the controlgrid. This spacing is difficult to control if the cathode moves relativeto the grid during operation of the tube.

Accordingly, it is a primary object of my invention to provide a new andimproved electrode support structure for a planar-type electrondischarge device which permits operation of the device at hightemperatures while maintaining precise spacing relationships between theelectrodes of the device.

It is another object of my invention to provide a new and improvedelectrode structure for a planar-type electron discharge device in whichthe cathode and control electrodes are supported by members whichaccommodate thermal expansion differentials without distortion of theelectrodes or contact members for the electrodes.

The features and advantages which characterize my invention will becomemore apparent as the following description proceeds, reference beingmade to the accompanying drawing and its scope will be pointed out inthe appended claims. In the drawing,

FIG. 1 is an elevation view, partly in section, of an electron dischargedevice embodying my invention; and

FIG. 2 is a sectionalperspective view of a portion of the device of FIG.1.

In the preferred embodiment illustrated, the envelope of the device ismade up of generally circular or annular metal and insulating membersalternately arranged and bonded together to provide a hermeticallysealed envelope. As illustrated in FIG. 1, the device includes agenerally circular anode 1 having a planar electron-receiving surface 2which is in opposed relation with the electron emissive surface of acathode 3. Cathode 3 may be of the type described and claimed in my ;.U.S. Pat. No. 3,334,263, granted Aug. 1, 1967 and assigned to theassignee of the present'invention, and consists of a large mass cathodemember having channels or recesses 4 for receiving transverse bars 5 ofa control grid 6. Grid 6 includes a support frame in the form of a metalannulus 7 and a plurality of fine grid conductors 8 which are welded orotherwise attached to the annulus 7 and bars 5. Bars 5 are relativelymassive compared to grid wires 8 and may be formed integrally withannulus 7.

The external portion of the envelope of the device is formed of aplurality of ceramic insulating cylindrical members bonded to metalcylindrical terminal members. The ceramic insulating members aredesirably Forsterite because of its low dielectric constant, or amagnesia and magnesia-alumina spinel, such as disclosed in US. Pat. No.3,1 13,846 Leschen, assigned to the assignee of this present invention.The ceramic cylinders 10, 11, 12, moreover, have the same coefficient ofexpansion as a titanium flange 13 which is sealed between cylinder 10and grid contact ring 14 which consists of any suitable contact metal,such as, for example, titanium.

Cylinder 11 is sealed between the lower surface of grid contact ring 14and a cathode contact ring 15 which, likewise, may comprise titanium.Cylinder 12 is sealed between cathode contact member 15 and a heatercontact member 16 which, likewise, may be formed of titanium. A pair ofconductors 17, 18 are connected respectively between cathode contact 15and heater contact 16 and the input terminals of a heater 19 mounted onthe lower surface of cathode 3. While any suitable heater may beemployed, the one illustrated is of the metalclad, insulated-type brazedto the lower surface of cathode 3 and which is disclosed and claimed inmy copending application Ser. No. 811,067 (Docket RD-2352)tiled Mar. 27,1969 and assigned to the assignee of this present invention.

In order to permit operation of the discharge device of my invention athigh frequencies over a wide range of output powers and, consequently,high temperatures for the cathode and control grid, I providetemperature compensating supports for both the control grid and thecathode. The temperature compensating support for the control gridcomprises a first corrugated metal ribbon 20 positioned between annulus7 and grid contact ring 14. The temperature compensating support forcathode 3 comprises a second corrugated metal ribbon 21 connectedbetween the outer edge of cathode 3 and the inner wall of thecylindrical cathode contact member 15. As illustrated, ribbon 21 restson the shoulder 22 provided on the inner wall of cylindrical cathodecontact member 15.

In selecting the materials for the temperature compensating support 20,a metal having a high coefficient of thermal conductivity is chosen sothat heat generated in the control grid is rapidly conducted throughbars 5 to annulus 7 and through corrugated ribbon 20 to grid contactmember 14. For this purpose, annulus 7 and bars 5 may comprise a metalselected from the group consisting of molybdenum and tungsten. Metalcontact ring 14 consisting of titanium and corrugated metal ribbon 20comprises molybdenum.

Since it is desired to operate and maintain cathode 3 at a hightemperature and to minimize loss of heat from the cathode, the materialselected for second corrugated ribbon 21 is chosen to have a lowcoefficient of thermal conductivity. Typically, cathode 3 is formed oftungsten and cathode contact ring 15 is formed of titanium. Accordingly,to minimize loss of heat from cathode 3 to cathode contact ring 15, Iform the second corrugated ribbon 21 of either tantalum or hafni- In theoperation of an electron discharge device according to my constructionat a high power output in the device, thermal expansion occurs in boththe grid and cathode members. However, by use of corrugated supportingribbon 20, the thermal expansion difference between the molybdenum ortungsten grid structure and the titanium contact ring is accommodatedwith no motion of the grid relative to the cathode. Similarly, by use ofcorrugated ribbon 21, thermal expansion of the cathode is accommodatedwithout any longitudinal movement of the cathode. By use of the twotemperature compensating supports, the relative motion between the gridand cathode surfaces are reduced to a minimum and thus the cathode andgrid may be spaced closely and precisely to obtemperature and outputpower.

While I have shown and described several embodiments of my invention, itwill be apparent to those skilled in the art that many changes andmodifications may be made without departing from my invention in itsbroader aspects and I, therefore, intend the appended claims to coverall such changes and modifications as fall within the true spirit andscope of my invention.

I claim:

1. In an electron discharge device of the type having a planar anode, anopposed planar cathode and a planar grid positioned between the anodeand the cathode, said grid comprising a metal annulus and a plurality ofwires connected across the opening in said annulus, atemperaturecompensating support for said grid comprising a metal contactring surrounding said annulus and having an inner wall inspaced-relationship with the outer wall of the annulus and a corrugatedmetal ribbon positioned between and in thermal contact with said walls,said ribbon comprising a metal having a high coeffi-- cient of thermalconductivity whereby heat generated in said grid wires and annulusduring operation of said device is-transmitted from said annulus throughsaid metal ribbon to said metal contact ring to prevent distortion anddisplacement of said grid.

2. In the device of claim 1 in which the annulus comprises a metalselected from the group consisting of molybdenum and tungsten and themetal of said contact ring comprises titanium, the corrugated metalribbon comprises molybdenum.

3. In the device of claim 2, an annulus which consists of molybdenum.

4. in the device of claim 2, an annulus which consists of tungsten.

5. In the device of claim 1, a cathode comprising a circular metalmember, a heater for said cathode, a cathode contact member encirclingsaid cathode comprising a metal cylinder having an inner wall in spacedrelation with the outer edge of said cathode member and a low thermalconductivity connection between said cathode and said contact membercomprising a second corrugated metal ribbon positioned between and inthermal contact with the inner wall of said cylinder and the outer edgeof said cathode member, said second ribbon comprising a metal having alow coefficient of thermal conductivity whereby heat loss from saidcathode to said cathode contact member is minimized.

6. In the device of claim 5 in which said cathode member comprisesmolybdenum, said cathode contact member comprises titanium, and saidsecond corrugated ribbon comprises tantalum or hafnium.

7. In the device of claim 5 in which said cathode member comprisestungsten, said cathode contact member comprises titanium, and saidsecond corrugatedribbon' comprises tantalum or hafnium.

8. ln the device of claim 6, said second corrugated ribbon comprisestantalum.

9. In the device of claim 7, said second corrugated ribbon comprisestantalum.

10. In the device of claim 2, a cathode comprising a circular metalmember, a heater for said cathode, a cathode contact member encirclingsaid cathode member comprising a metal cylinder having an inner wall inspaced relationship with the outer edge of said cathode member, and alow thermal conductivity connection between said cathode and saidcontact member comprising a second corrugated metal ribbon positionedbetween and in thermal contact with the inner wall of said cylinder andthe outer edge of said cathode member, said second ribbon comprising ametal having a low coefficient of thermal conductivitywhereby heat lossfrom said cathode to said cathode contact member is minimized.

11. In the device of claim 10, said cathode member comprises molybdenum,said cathode contact member comprises titanium, and said secondcorrugated ribbon comprises a metal selected from the group-consistingof tantalum or hafnil2. In the device of claim 11, said cathode membercomprises tungsten, said cathode contact member comprises titanium, andsaid second corrugated ribbon comprises a metal selected from the groupconsisting of tantalum or hafnium.

13. In the device of claim 2, said corrugated metal ribbon is brazed tosaid annulus by a metal selected from the group consisting of gold andcopper and is brazed to said metal contact member by an alloy selectedfrom the group consisting of nickel-titanium and copper-titanium.

14. In an electron discharge device having a pair of spaced opposedplanar electrodes, a temperature compensating support for one of saidelectrodes comprising a cylindrical member surrounding and in spacedrelation with said one electrode and a corrugated metal ribbonpositioned between and fastened to the outer edge of said electrode andin the inner wall of said cylindrical member, whereby lateral expansionof said electrode during high temperature operation of the device isabsorbed by said ribbon without distorting or displaying said electrode.

1. In an electron discharge device of the type having a planar anode, anopposed planar cathode and a planar grid positioned between the anodeand the cathode, said grid comprising a metal annulus and a plurality ofwires connected across the opening in said annulus, a temperaturecompensating support for said grid comprising a metal contact ringsurrounding said annulus and having an inner wall in spaced relationshipwith the outer wall of the annulus and a corrugated metal ribbonpositioned between and in thermal contact with said walls, said ribboncomprising a metal having a high coefficient of thermal conductivitywhereby heat generated in said grid wires and annulus during operationof said device is transmitted from said annulus through said metalribbon to said metal contact ring to prevent distortion and displacementof said grid.
 2. In the device of claim 1 in which the annulus comprisesa metal selected from the group consisting of molybdenum and tungstenand the metal of said contact ring comprises titanium, the corrugatedmetal ribbon comprises molybdenum.
 3. In the device of claim 2, anannulus which consists of molybdenum.
 4. In the device of claim 2, anannulus which consists of tungsten.
 5. In the device of claim 1, acathode comprising a circular metal member, a heater for said cathode, acathode contact member encircling said cathode comprising a metalcylinder having an inner wall in spaced relation with the outer edge ofsaid cathode member and a low thermal conductivity connection betweensaid cathode and said contact member comprising a second corrugatedmetal ribbon positioned between and in thermal contact with the innerwall of said cylinder and the outer edge of said cathode member, saidsecond ribbon comprising a metal having a low coefficient of thermalconductivity whereby heat loss from said cathode to said cathode contactmember is minimized.
 6. In the device of claim 5 in which said cathodemember comprises molybdenum, said cathode contact member comprisestitanium, and said second corrugated ribbon comprises tantalum orhafnium.
 7. In the device of claim 5 in which said cathode membercomprises tungsten, said cathode contact member comprises titanium, andsaid second corrugated ribbon comprises tantalum or hafnium.
 8. In thedevice of claim 6, sAid second corrugated ribbon comprises tantalum. 9.In the device of claim 7, said second corrugated ribbon comprisestantalum.
 10. In the device of claim 2, a cathode comprising a circularmetal member, a heater for said cathode, a cathode contact memberencircling said cathode member comprising a metal cylinder having aninner wall in spaced relationship with the outer edge of said cathodemember, and a low thermal conductivity connection between said cathodeand said contact member comprising a second corrugated metal ribbonpositioned between and in thermal contact with the inner wall of saidcylinder and the outer edge of said cathode member, said second ribboncomprising a metal having a low coefficient of thermal conductivitywhereby heat loss from said cathode to said cathode contact member isminimized.
 11. In the device of claim 10, said cathode member comprisesmolybdenum, said cathode contact member comprises titanium, and saidsecond corrugated ribbon comprises a metal selected from the groupconsisting of tantalum or hafnium.
 12. In the device of claim 11, saidcathode member comprises tungsten, said cathode contact member comprisestitanium, and said second corrugated ribbon comprises a metal selectedfrom the group consisting of tantalum or hafnium.
 13. In the device ofclaim 2, said corrugated metal ribbon is brazed to said annulus by ametal selected from the group consisting of gold and copper and isbrazed to said metal contact member by an alloy selected from the groupconsisting of nickel-titanium and copper-titanium.
 14. In an electrondischarge device having a pair of spaced opposed planar electrodes, atemperature compensating support for one of said electrodes comprising acylindrical member surrounding and in spaced relation with said oneelectrode and a corrugated metal ribbon positioned between and fastenedto the outer edge of said electrode and in the inner wall of saidcylindrical member, whereby lateral expansion of said electrode duringhigh temperature operation of the device is absorbed by said ribbonwithout distorting or displaying said electrode.